1. Reference to Microfiche Appendix
Microfiche Appendix A of 2 sheets and 75 frames and microfiche Appendix B of 1 sheet and 58 frames are part of the present disclosure, and are incorporated herein by reference in their entirety.
Microfiche Appendices A and B include VERILOG code listings for generating the modules for a serial port for a host adapter integrated circuit and a slave serial port input-output integrated circuit respectively.
A portion of the disclosure of this patent document contains material which is subject to copyright protection. The copyright owner has no objection to the facsimile reproduction by anyone of the patent document or the patent disclosure, as it appears in the Patent and Trademark Office patent files or records, but otherwise reserves all copyright rights whatsoever.
2. Field of the Invention
The present invention is related generally to a serial port for an integrated circuit and in particular to a serial port for input and output of information to a circuit external to the integrated circuit using a single pin terminal of the integrated circuit.
3. Description of Related Art
As the number of functions performed by an integrated circuit, hereinafter IC, increases, typically the number of pins of the integrated circuit also increases. However, as a rule of thumb, a packaged integrated circuit with a large number of pins is more expensive to fabricate than an IC with relatively fewer pins. Also, a large number of pins adds to the cost of the board on which the IC is to be mounted. Packaged ICs with a large number of pins at the periphery cannot be used due to lack of real estate on the board. Packaged ICs with multiple rows of pins inside the periphery at the bottom of the package require additional layers in a board and increase complexity of interconnects on the board. The number of pins of an IC can also impose a limit on the number of functions that can be performed in the IC.
When an IC, such as host adapter 112A that interfaces an input-output bus, e.g. SCSI bus, to a host computer's system bus, e.g. PCI bus, (FIG. 1A) is mounted on a plug-in board 110, the number of pins needed by host adapter 112A is not constrained in a majority of cases. Host adapter 112A (FIG. 1A) has a number of pins, such as pins 112-1, 112-2, . . . 112-N to support an adapter read-only-memory 111 for basic input-output software, hereinafter BIOS of host adapter 112A.
External logic (not shown) is needed by some host adapters to support adapter read-only-memory 111. For example, "36C70 SCSI IC Technical Reference Manual" by Future Domain Corporation, 2801 McGraw Avenue, Irvine, Calif. 92714, November 1993, discloses a host adapter in which "a! minimal amount of external glue logic is required to serialize the parallel ROM data" (page 3-1). During system start-up, the information from the adapter read-only-memory can be copied into system memory 170 for quick access by host processor 161, sometimes referred to as microprocessor 161.
In contrast, when a host adapter 112B (FIG. 1B) is mounted on a-mother board 160 of a personal computer, the number of pins of host adapter 112B can be limited to, for example, 100 pins due to less real estate available on mother board 160 as compared to plug-in board 110. Host adapter 112B eliminates the need for a connector that is otherwise necessary for a plug-in board. Host adapter 112B (FIG. 1B) does not have pins to access adapter read-only-memory 111, e.g. pins 112-1, 112-2, . . . 112-N of host adapter 112A (FIG. 1A). BIOS for host adapter 112B is loaded from processor read-only-memory 162 that also contains the system BIOS for microprocessor 161. Thus host adapter 112B is limited to performing only certain basic functions, such as data transfer between system bus 120 and input-output bus 140. Such a host adapter 112B cannot be used on plug-in board 110 e.g. if host adapter 112B does not support a read-only-memory.
A way is needed for a limited pin integrated circuit, such as host adapter 112B to use resources, such as a read-only-memory, without increasing the number of pins, so that the same host adapter 112B can be used on both a mother board and a plug-in board.